Cleaning up Resources


The latest version of this topic can be found at Cleaning up Resources.

During termination-handler execution, you may not know which resources are actually allocated before the termination handler was called. It is possible that the __try statement block was interrupted before all resources were allocated, so that not all resources were opened.

Therefore, to be safe, you should check to see which resources are actually open before proceeding with termination-handling cleanup. A recommended procedure is to:

  1. Initialize handles to NULL.

  2. In the __try statement block, allocate resources. Handles are set to positive values as the resource is allocated.

  3. In the __finally statement block, release each resource whose corresponding handle or flag variable is nonzero or not NULL.

For example, the following code uses a termination handler to close three files and a memory block that were allocated in the __try statement block. Before cleaning up a resource, the code first checks to see if the resource was allocated.

// exceptions_Cleaning_up_Resources.cpp  
#include <stdlib.h>  
#include <malloc.h>  
#include <stdio.h>  
#include <windows.h>  
void fileOps() {  
   FILE  *fp1 = NULL,  
         *fp2 = NULL,  
         *fp3 = NULL;  
   LPVOID lpvoid = NULL;  
   errno_t err;  
   __try {  
      lpvoid = malloc( BUFSIZ );  
      err = fopen_s(&fp1, "ADDRESS.DAT", "w+" );  
      err = fopen_s(&fp2, "NAMES.DAT", "w+" );  
      err = fopen_s(&fp3, "CARS.DAT", "w+" );  
   __finally {  
      if ( fp1 )  
         fclose( fp1 );  
      if ( fp2 )  
         fclose( fp2 );  
      if ( fp3 )  
         fclose( fp3 );  
      if ( lpvoid )  
         free( lpvoid );  
int main() {  

Writing a Termination Handler
Structured Exception Handling (C/C++)